bonded to a negatively charge carbon atom. To form a ylide, a triphenylphosphine attacks a primary or secondary alkyl halide to form phosphonium salt which is deprotonated. To obtain the desired product in a Wittig reaction, the carbonyl compound is treated with a ylide which forms a four-member ring called oxaphosphetane. The second step is to make a more stable bond, to achieve this an elimination occurs to form Ph3P=O (triphenylphosphine oxide) and as a result, forms the alkene. The alkene can come
(derived from phosphonium salt).The mechanism for the synthesis of trans-9-(2-phenylethenyl) anthracene first requires the formation of the phosphonium salt by the addition of triphenylphosphine and alkyl halide. The phosphonium halide is produced through the nucleophilic substitution of 1° and 2° alkyl halides and triphenylphosphine (the nucleophile and weak base) 4 An example is benzyltriphenylphosphonium chloride which was used in this experiment. The second step in the formation of the of the Wittig
Discussion: The synthesised ethyl cinnamate weighed 0.56 g, which was equivalent to 140% of the theoretical yield of 0.414 g. This excessive yield was resultant of the impurities within the product, where the solvents, particularly the dichloromethane, were not sufficiently removed from the product. In figure 3, the peak at 5.22 ppm with a normalised intensity of 1.00 evidenced the significant proportion of the dichloromethane in the product, and the peak at 0.88 ppm with a normalised intensity of
The Chemical Synthesis of Oligonucleotides and the Phosphoramidite Method By Klaus D. Linse The study of nucleic acids has now become a fruitful and dynamic scientific enterprise. Nucleic acids are of unique importance in biological systems. Genes are made up of deoxyribonucleic acid or DNA, and each gene is a linear segment, or polymer, of a long DNA molecule. A DNA polymer, or DNA oligonucleotide, contains a linear arrangement of subunits called nucleotides. There are four types of nucleotides